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Understanding Colorectal Cancer

the Basics

What Is Colorectal Cancer?

Inside your abdominal cavity is the long, tubular digestive tract. The second part of this tube -- the large intestine -- is composed of the colon, which stretches four to six feet, and the rectum, which is only four to six inches long. The inner lining of this "colorectal tube" can be a fertile breeding ground for small tumors, called polyps (Figure 1). About a quarter of all adults in the U.S. over the age of 50 will have at least one colorectal polyp. Most colorectal cancers develop from polyps in glandular tissue of the intestinal lining.

Most polyps are benign, but at least one type is known to be precancerous. Most colorectal cancers develop from polyps in glandular tissue of the intestinal lining.

If colorectal cancer is diagnosed and treated early while the tumor is still localized, the disease is highly curable, with five-year survival rates of about 90%. If the tumor continues to grow, cancer can spread directly through the bowel wall to surrounding tissues and organs, as well as into the bloodstream or lymphatic system.

Once the cancer spreads to lymph nodes or other organs, successful treatment becomes more difficult. Depending on how advanced the disease is, five-year survival rates range from 65% to 9%.

Cancers of the colon and rectum are the third most common cancer in the U.S., with approximately 150,000 cases diagnosed each year. Like many cancers, colorectal cancer is of particular concern for people older than age 50.

Although detection is often possible at an early stage, many people delay seeking medical care because they are embarrassed or fearful of symptoms related to their bowels. Risk increases significantly after age 50 and continues to increase with age.

What Causes Colorectal Cancer?

The exact cause of colorectal cancer is not known. But there are several risk factors for the disease.

• Other diseases. Colorectal cancer is strongly associated with certain other diseases. Those people considered at high risk include anyone with a personal or family history of colon polyps, inflammatory disease of the colon such as ulcerative colitis or Crohn's disease, and cancers of the pancreas, breast, ovaries, or uterus.
• Heredity. As with any cancer, susceptibility to colorectal cancer is at least partly determined by genetic makeup. A few people inherit medical conditions familial adenomatous polyposis (FAP) or Gardner's syndrome, in which colon polyps develop at an early age; unless treated, these people are almost certain to develop colorectal cancer.
• Hereditary nonpolyposis colon cancer.
• Diet. Diet also contributes to the risk, although the cause-and-effect relationship is still unclear. People whose diets are high in fruits and vegetables seem to have a reduced risk. Many studies implicate animal fat and protein as promoters of colorectal cancer, although researchers are cautious about drawing any definite conclusions. Some studies show that regularly eating red meat, which is rich in saturated fat and protein, increases risk, while others find no connection. Some scientists think that fat is the main culprit, while others suspect protein. Others contend that it's not the fat and protein themselves, but the way they are cooked. They note that fats and protein cooked at high temperatures -- especially when broiled and barbecued -- can produce a host of potentially carcinogenic substances linked to colorectal cancer.
• Chemical Exposure. Heavy exposure to certain chemicals, including chlorine -- which in small amounts is commonly used to purify drinking water -- may increase the risk of colorectal cancer. Exposure to asbestos is throught to be potentially harmful because it has been implicated in causing formation of polyps in the colon.

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